The present invention relates to a method of conformance testing of a radio communication system during soft handover, and to a radio test equipment for carrying out the method. While the present specification describes the method with particular reference to the emerging Universal Mobile Telecommunication System (UMTS), it is to be understood that such techniques are equally applicable to use in testing equipment for other mobile radio systems.
There are two basic types of communication required between a Base Station (BS) and a Mobile Station (MS) in a radio communication system. The first is user traffic, for example speech or packet data. The second is control information, required to set and monitor various parameters of the transmission channel to enable the BS and MS to exchange the required user traffic.
In many radio communication systems accurate power control is important. This is particularly so in systems employing spread spectrum Code Division Multiple Access (CDMA) techniques, because many communication channels share the same bandwidth and so transmission at too high a power in any one channel reduces the signal to noise ratio in all the other channels. Uplink power control, of signals transmitted to a Base Station (BS) from a Mobile Station (MS), is particularly important. It ensures that the BS receives signals from different MSs at approximately the same power level, while minimising the transmission power required by each MS. Downlink power control, of signals transmitted by the BS to a MS, is required so that the MS receives signals from the BS with a low error rate while minimising transmission power, to reduce interference with other cells and radio systems.
In a UMTS embodiment, power control is normally operated in a closed loop manner. For uplink power control the BS determines the required changes in the power of transmissions from a MS and signals these changes to the MS by means of Transmit Power Control (TPC) commands. To minimise overheads, a TPC command typically instructs the MS to increase or decrease its power, with the change in power being a step of predetermined size. However, in some systems a TPC command may also determine the step size to be used.
A MS generally communicates with a single BS. During the course of a call the MS may wish to investigate transferring to another BS, for example when the quality of the communication link deteriorates as the MS moves away from its BS, or when the relative traffic loading of different cells requires adjusting. The process of transferring from one BS to another is known as handover. In a version of this process known as soft handover, the MS engages in communication with a plurality of BSs (known as the xe2x80x9cactive setxe2x80x9d of BSs) to determine to which BS, if any, it should transfer. When the MS is engaged in this process, it will receive TPC commands from each of the BSs at substantially the same time. It must therefore have an algorithm for determining how to handle a plurality of TPC commands, which may be conflicting.
In one algorithm, which must be supported by a MS suitable for use in a UMTS system, the MS assesses the reliability of the TPC command from each BS when deciding how to adjust its transmission power. Methods for performing this assessment include measuring the Signal-to-Interference Ratio (SIR) of the received TPC commands, measuring the SIR of other symbols within the same timeslot (for example pilot symbols), and measuring the actual received signal amplitude of the TPC bits before decoding, a function of which amplitudes may be known as Soft Symbol Information (SSI).
To determine whether a MS is suitable for use in a particular communication system, such as UMTS, it must undergo conformance tests to determine whether its operation complies with the relevant standards. In such a conformance test to analyse whether a MS is correctly processing TPC commands while performing a soft handover, it is difficult to access the result of the MS""s estimation of SIR or SSI. Hence it is difficult to assess whether the MS""s behaviour is correct.
An object of the present invention is to provide a method of conformance testing of radio communication equipment during soft handover which addresses the above problem. A further object of the present invention is to enable the required behaviour of radio communication equipment during soft handover to be specified.
According to a first aspect of the present invention there is provided a method for conformance testing of a secondary station for use in a radio communication system, the secondary station having means for engaging in a soft handover process in which it communicates with at least two primary stations simultaneously and also having power control means for adjusting its output transmission power in response to power control commands received from each of the at least two primary stations, the method comprising operating in a test equipment the steps of:
generating and transmitting to a secondary station under test at least two signals equivalent to those transmitted by each of the at least two primary stations, each signal including a sequence of power control commands;
monitoring the output transmission power of the secondary station; and
determining whether a function of the output transmission power is within its specified tolerance.
According to a second aspect of the present invention there is provided a radio test equipment for conformance testing of a secondary station for use in a radio communication system, the test equipment being adapted to carry out the test method according to a first aspect of the present invention.
By means of the present invention there is provided a method of conformance testing of a MS processing TPC commands during soft handover.